1. Field of the Invention
The present invention relates to a heater unit structure of an air mixing apparatus for an automotive vehicle, and more specifically to a heater unit structure which can improve the workability of various vent duct assemblies.
2. Description of the Prior Art
In general, an air mixing apparatus for an automotive vehicle includes a blower unit for introducing inside air and outside air, a cooling unit having a cooling heat exchanger, and a heater unit case having a heating heat exchanger and various air blowing outlets. Inside air and outside air introduced through the blower unit are mixed with each other when passing through the cooling and heating heat exchangers, and the mixed air is blown out into the vehicle room through various air blowing outlets.
FIG. 1A shows an example of the conventional structure of the heater unit, which includes a core case 101 having a heating heat exchanger 103 (e.g. heater core), and an air distribution case 105 connectable to a vent duct 107, a defroster duct 109, and a foot duct 111, respectively. Two side vent ducts 113 extending between the driver seat side and the front passenger seat side are usually formed integral with the vent duct 107. Therefore, when the vent door 115, the defroster door 117 and the foot door 119 are pivoted from the respective solid line positions to the respective dot-dot-dashed line positions or vice versa, well mixed air can be selectively blown out through the respective blowing outlets of the respective ducts 107, 109, 111 and 113, as disclosed in Japanese Published Unexamined (Kokai) Patent Appli. No. 62-286823, for instance.
In the prior-art heater unit structure, the assembly procedure is as follows: the heater unit is fixed to the vehicle body; the respective ducts 107, 109 and 111 are attached to the distribution case 105; the instrument panel 127 is fixed to the vehicle body; and the defroster ducts 109 are finally attached to opening portions 129 of the instrument panel 127.
In the above-mentioned prior-art heater unit, however, since the side vent duct 113 is formed integral with the vent duct 107 in such a way as to extend to the driver seat side as shown in FIG. 1B, there exists a problem in that a post bracket 123 for supporting a steering member 121 extending in the vehicle transverse direction interferes with the side vent duct 113 extending to the driver seat side, and therefore the side vent duct 113 becomes complicated in shape because the side vent duct 113 must be arranged through a space enclosed by the post bracket 123, a steering member 121, and a steering column 125.
Accordingly, although the assembly work can be completed by attaching the respective ducts 107, 109, and 111 to the distribution case 105 before attaching the instrument panel 127, there exists a problem in that it takes much time to attach each duct one by one to the distribution case 105 and therefore the assembly productivity is extremely low. In addition, since the instrument panel 127 is large in size and therefore easily deformable in shape, a troublesome assembly work is required to fit a blowing outlet 131 of the defroster duct 109 (for blowing out air toward the windshield 133) to the opening portion 129 of the instrument panel 127. In this assembly work, if the respective ducts 107 and 109 can be first attached to the instrument panel 127, it may be possible to improve the workability of duct assembly between the blowing outlets 131 of the defroster ducts 109 and the openings 129 formed in the instrument panel 127. In this case, however, since the side vent duct 113 formed integral with the vent duct 107 and extending to the driver seat side is complicated in shape there exists a problem in that it is impossible to first attach the respective ducts 109 and 107 to the instrument panel 127. The above-mentioned problem is serious in particular, when the heater unit is mounted on a vehicle body in a full automatic assembly process line.